The present invention relates to a back lighting device for liquid-crystal panels that illuminates transmissive or semi-transmissive panels from the rear side.
Thin liquid-crystal display's provided with a backlighting mechanism that allows easy viewing of information on the screen are used with recent versions of lap-top or book type word processors and computers. The backlighting mechanism in common use adopts an "edge lighting" method in which a linear light source such as a fluorescent tube is provided at one end portion of a transmissive light conducting plate as shown in FIG. 1. Further, as shown in FIG. 2, one surface of the light conducting plate operating on the edge lighting method is often covered partially with a light diffusing material having a higher refractive index than the material of which said light conducting plate is made and the thus covered area is almost entirely covered with a specular reflecting or light diffusing/reflecting plate.
In addition, as is often the case today, back lighting devices are driven with a battery and a further improvement in the efficiency of power to luminance conversion is desired. To meet this need, it has been proposed that a light reflector covering the linear light source be provided with a light reflecting plate having high light reflectance.
The methods described above achieve some improvement in the efficiency of power to luminance conversion but it is still insufficient and an even better improvement is desired.